Power transmission shafts — on motors and gearboxes, for example — are subjected to torque loads that result in torsion, or twisting of the shaft about its axis. Similar to structures under tension or compression, two important mechanical properties of shafts under torque loads are shear stress and shear strain. Stress is a material’s resistance […]
Ball + lead + roller screws
Ball screw standards: What you need to know about DIN, ISO, and JIS
If you’re involved in ball screw sizing or selection, you’ve probably noticed that there are several different standards that govern various aspects of ball screw design, from lead accuracy and load capacity to ball nut tolerances and rigidity. Fortunately, in many cases, these standards are in harmony and provide the same (or virtually equivalent) specifications. […]
Tribology basics for linear bearings
Tribology is the study and application of the principles of friction, lubrication, and wear between two surfaces in relative motion. In linear bearing systems, those two surfaces are the bearing element and the guide raceway. Friction and wear The term “wear” generally refers to deterioration, but when discussing tribology principles in relation to bearings, it refers […]
How to specify linear motion components for vacuum applications
Vacuum applications are common in the manufacturing of semiconductors, liquid crystal and plasma displays, fiber optics, and aerospace components, where linear motion systems are used for the positioning, handling, and alignment of critical equipment. Although vacuum applications are often likened to cleanroom applications, in the category of “special environments,” there is a critical difference between […]
THK to show low-inertia ballscrew-spline BNS-V during IMTS
In two weeks, IMTS visitors will be able to see THK’s ballscrew-spline BNS-V at booth #134514. Featuring an exceptionally compact and lightweight structure, the low-inertia BNS-V enables quick starts and stops during high-speed operation. The BNS-V is a stroke-rotary unit with ball screw grooves and a ball spline groove that cross one another on a […]
What are the benefits of a rotating ball nut (aka driven nut)?
When you think of a ball screw assembly, you probably envision a screw shaft with a motor connected to one end. The motor turns the screw, and the ball nut travels along the length of the screw shaft. An alternative setup is to hold the screw shaft stationary and rotate, or drive, the ball nut […]
What’s the difference between dynamic load capacity and static load capacity?
Rolling element linear bearings, such as round shafts and bushings, profiled rail guides, crossed roller slides, and even ball screws, have two load capacity specifications — dynamic load capacity and static load capacity — which are based on different operating parameters and performance criteria and are independent of each other. To accurately size and select a […]
When should you lubricate a lead screw?
It’s expected that a ball screw, with metal-on-metal rolling contact between the balls and the raceways, will require periodic lubrication with either grease or oil. One of the advantages that lead screws have over ball screws is that they can often operate without lubrication — eliminating maintenance and the potential hazards that come with using […]
How to calculate the effect of preload on ball screw axial deflection
In a recent post, we looked at the methods for inducing preload in a ball screw assembly and the effects it has on performance. One of those effects is that preload reduces axial deflection (displacement) and increases rigidity. But preload also increases the applied load on the screw assembly and reduces life. To determine the […]
Ball screw preload: What you need to know
When a linear motion application requires high thrust force and rigidity along with good positioning accuracy, a preloaded ball screw assembly is often the best choice. Manufacturers offer ball screw preload amounts ranging from just 1 or 2 percent for applications where backlash would be detrimental, up to 10 percent or greater for applications that […]
